In a separate development, Syrian Kurdish militia YPG says it will exit Manbij in a move which will allow it to be part of an offensive against Daesh in the city of Raqqa.
Turkey-backed Free Syrian Army (FSA) is just two kilometres (1.25 miles) from the northern Syrian city of al-Bab and is expected to take it quickly from Daesh despite some resistance, Turkish President Recep Tayyip Erdogan said on Wednesday.
The FSA said on Tuesday it had taken Qabasin, several kilometres northeast of al-Bab, setting the stage for an assault on the last urban stronghold of Daesh in the northern Aleppo countryside.
"The Free Syrian Army, with the support of our special forces, is about two kilometres away and the siege is continuing as planned," Erdogan told a news conference in Ankara before departing on an official visit to Pakistan.
"There is resistance now, but I don't think it will last much longer," he said.
YPG retreats east of Euphrates
YPG will pull out from the Syrian city of Manbij and withdraw east of the Euphrates River. This move will allow the YPG to participate in the campaign to liberate the Daesh-stronghold of Raqqa, it said in a statement.
YPG is the armed wing of the PYD, whose principal aim is to carve out an autonomous region in northern Syria. Turkey has repeatedly called for the YPG to withdraw east of the Euphrates – where Raqqa lies.
Ankara views the militia as a hostile force with affiliated with the PKK, which is designated as a terror group and has fought a bloody three-decade insurgency on Turkish soil. Ankara remains unhappy with Washington's support of the YPG.
US special envoy Brett McGurk described the move as a "milestone", saying on Twitter that all YPG units would depart Manbij after training local units to maintain the city's security against Daesh.
Ankara has also said YPG fighters, part of the US-supported Syrian Democratic Forces, should not be involved in the planned Raqqa offensive.
On November 8, Foreign Minister Mevlut Cavusoglu said Turkey wants to ensure that the "wrong groups" do not take part in the operation to push Daesh from Raqqa
Cavusoglu told a news conference that the United States had told Turkey that such groups—a reference to the YPG—would only take part in the siege of Raqqa and not enter the city.
But he said Turkey was "taking measures" after its partners did not keep promises regarding the Syrian city of Manbij, from where Turkey has repeatedly said the YPG must withdraw.
The Raqqa offensive is expected within weeks.
Turkey sent warplanes, tanks and artillery into Syria in August in an operation dubbed "Euphrates Shield" which was meant to drive both Daesh and Kurdish militia forces away from its border.